Embryo transfer as a means of controlling the transmission of viral infections. II. The in vitro exposure of preimplantation bovine embryos to infectious bovine rhinotracheitis virus

Bovine embryos, at the 16-cell to the blastocyst stage of development, were exposed to infectious bovine rhinotracheitis virus (IBRV) for either one or 24 hours. These embryos were then washed and incubated for 24 or 48 hours before being assayed for IBRV. Under these conditions, infectious virus at the level of 0-10(2.2) TCID(50)/ml was isolated from 57-64% of the embryos exposed to IBRV. Trypsin and IBRV-antiserum were found to be capable of removing and/or inactivating the IBRV from exposed embryos. Both the low level of the virus isolated from these embryos and the susceptibility of this virus to trypsin and antiserum suggests that IBRV attaches to the zona pellucida of embryos and cannot penetrate this structure to gain access to the embryonic cells. IBRV was found to have no effect on embryonic development in vitro . In addition, thirty-one eggs/embryos isolated from donors that were seropositive to IBRV were found to be uninfected with this virus.